A patient in the ICU has the following hemodynamic data: CVP 14 mmHg, PCWP 22 mmHg, CO 3.2 L/min, SVR 1800 dynes-sec/cm5. This profile is MOST consistent with:

Cardiogenic shock. This hemodynamic profile shows elevated filling pressures (high CVP and PCWP), low cardiac output, and elevated SVR — the classic pattern of cardiogenic shock. The heart is failing as a pump, causing blood to back up (high pressures), reduced forward flow (low CO), and compensatory vasoconstriction (high SVR).

During CPR, the ETCO2 suddenly increases from 12 mmHg to 38 mmHg. This MOST likely indicates:

Return of spontaneous circulation (ROSC). A sudden, sustained rise in ETCO2 during CPR strongly suggests return of spontaneous circulation (ROSC). When the heart begins pumping effectively, it delivers more CO2-rich blood to the lungs, causing ETCO2 to increase. Low ETCO2 during CPR reflects poor cardiac output; a sudden rise indicates restored circulation.

A firefighter is rescued from a burning building with an SpO2 reading of 99%. The RT should recognize that this reading may be:

Falsely elevated due to carbon monoxide poisoning. Standard pulse oximeters cannot distinguish between oxyhemoglobin (O2-bound) and carboxyhemoglobin (CO-bound). In carbon monoxide poisoning, SpO2 reads falsely high because carboxyhemoglobin is detected as oxyhemoglobin. A CO-oximeter is needed for accurate assessment. Treatment is 100% oxygen via non-rebreather mask.

Which of the following conditions would cause a FALSELY normal SpO2 reading despite inadequate oxygen delivery?

Severe anemia. In severe anemia, the hemoglobin that IS present may be fully saturated (normal SpO2), but the total hemoglobin is too low to deliver adequate oxygen to tissues. SpO2 measures the PERCENTAGE of hemoglobin saturated, not the total oxygen content. A patient with an Hgb of 5 g/dL may have an SpO2 of 98% but critically low oxygen delivery.

1.3 Hemodynamic Monitoring & Waveform Analysis | CRT/RRT Respiratory Therapist Exam | Free Exam Prep

Key Takeaways

Central venous pressure (CVP) normal is 2-6 mmHg; elevated CVP suggests right heart failure, fluid overload, or tension pneumothorax
Pulmonary artery pressure (PAP) normal is 25/10 mmHg (systolic/diastolic), mean 15 mmHg
Pulmonary capillary wedge pressure (PCWP) normal is 6-12 mmHg; elevated suggests left heart failure
Normal cardiac output (CO) is 4-8 L/min; cardiac index (CI) normal is 2.5-4.0 L/min/m2
Pulse oximetry (SpO2) normal is 95-100%; readings may be inaccurate with carbon monoxide poisoning, poor perfusion, or nail polish
End-tidal CO2 (ETCO2) normal is 35-45 mmHg; used to confirm ET tube placement, monitor ventilation, and detect ROSC
Ventilator waveform analysis identifies auto-PEEP, patient-ventilator asynchrony, and air trapping
Mixed venous oxygen saturation (SvO2) normal is 60-80%; values below 60% indicate inadequate oxygen delivery

Hemodynamic Monitoring & Waveform Analysis

Hemodynamic monitoring provides critical data about cardiovascular function and oxygen delivery. Respiratory therapists must understand these parameters because respiratory interventions (mechanical ventilation, PEEP, oxygen therapy) directly affect hemodynamics. The TMC exam tests your ability to interpret hemodynamic data and correlate it with clinical conditions.

Hemodynamic Parameters — Normal Values and Clinical Significance

Parameter	Normal Range	Elevated In	Decreased In
CVP (Central Venous Pressure)	2-6 mmHg	Right heart failure, fluid overload, tension pneumothorax, cardiac tamponade	Hypovolemia, dehydration
PAP (Pulmonary Artery Pressure)	Systolic 15-25 mmHg, Diastolic 8-15 mmHg, Mean 10-20 mmHg	Pulmonary hypertension, left heart failure, COPD, PE, ARDS	Hypovolemia
PCWP (Pulmonary Capillary Wedge Pressure)	6-12 mmHg	Left heart failure (>18 = cardiogenic pulmonary edema), mitral valve disease	Hypovolemia
CO (Cardiac Output)	4-8 L/min	Sepsis (early), exercise, fever	Heart failure, cardiogenic shock, hypovolemia
CI (Cardiac Index)	2.5-4.0 L/min/m2	Same as CO, normalized for body size	Same as CO
SVR (Systemic Vascular Resistance)	800-1200 dynes-sec/cm5	Cardiogenic shock, hypothermia	Septic shock (warm phase), anaphylaxis
PVR (Pulmonary Vascular Resistance)	150-250 dynes-sec/cm5	Pulmonary hypertension, hypoxic vasoconstriction, ARDS	Pulmonary vasodilators
SvO2 (Mixed Venous O2 Saturation)	60-80%	Increased O2 delivery, decreased demand	Shock, decreased CO, anemia, increased O2 consumption

Distinguishing Hemodynamic Profiles

Condition	CVP	PCWP	CO	SVR
Cardiogenic shock	High	High	Low	High
Hypovolemic shock	Low	Low	Low	High
Septic shock (warm)	Low	Low	High	Low
Right heart failure	High	Normal/Low	Low	High
Cardiac tamponade	High	High	Low	High

Pulse Oximetry (SpO2)

Pulse oximetry is the most commonly used non-invasive monitoring tool:

Normal SpO2: 95-100% (goal >88-92% in COPD patients to avoid suppressing hypoxic drive)
Mild hypoxemia: SpO2 90-94%
Moderate hypoxemia: SpO2 85-89%
Severe hypoxemia: SpO2 <85%

Limitations of Pulse Oximetry:

Carbon monoxide poisoning: SpO2 falsely elevated (carboxyhemoglobin reads as oxyhemoglobin)
Methemoglobinemia: SpO2 trends toward ~85% regardless of actual saturation
Poor perfusion: Low cardiac output, vasoconstriction, hypothermia cause unreliable readings
Dark nail polish or artificial nails: May interfere with light absorption
Motion artifact: Patient movement creates erratic readings
Anemia: SpO2 may be normal despite inadequate oxygen content

Capnography (ETCO2)

End-tidal CO2 monitoring measures the CO2 concentration at the end of exhalation:

Normal ETCO2: 35-45 mmHg (should be close to PaCO2)
Primary uses: ET tube placement confirmation, ventilation adequacy monitoring, CPR quality, ROSC detection
Elevated ETCO2: Hypoventilation, increased CO2 production (fever, sepsis), rebreathing
Decreased ETCO2: Hyperventilation, decreased cardiac output, PE, circuit disconnect
Absent ETCO2: Esophageal intubation, cardiac arrest (no blood flow), circuit disconnect

CRT/RRT Respiratory Therapist Exam

1Introduction: NBRC TMC Exam Overview

2Chapter 1: Patient Data Evaluation

3Chapter 2: Airway Management & Oxygen Therapy

4Chapter 3: Mechanical Ventilation

5Chapter 4: Pharmacology & Equipment

6Chapter 5: Infection Control, Ethics & Professional Practice